Piston wrist pins are traditionally made from hollow hardened steel members, and a wrist pin is closely fitted into a piston made of softer metal, such as an aluminum alloy. It is necessary to force the wrist pin into the bore of the connecting rod and, during this operation, the piston is conventionally subjected to strong clamping pressure in order to force the wrist pin in or out of the eye of the connecting rod. Prior practice resulted in distortion or damage to the connecting rod eye, through which the wrist pin is forced, or to the piston.
Known patents, such as Fuglie et al., U.S. Pat. No. 2,891,302, and Schneider, U.S. Pat. No. 4,118,852, show devices having a press pin with an end section of reduced diameter which enters into the bore of the upper end of a wrist pin. Neither of these two patents, nor other patents directed to this subject matter, for example, De Martelaere, U.S. Pat. No. 4,118,851, Sunnen, U.S. Pat. No. 2,887,768, Stein, U.S. Pat. No. 3,031,744, Simmons, U.S. Pat. No. 3,111,752, Okamuro, U.S. Pat. Nos. 4,050,139 and 4,073,051, show a guide pin having an end section of reduced diameter, which enters into the lower end of a bore of a wrist pin to guide the wrist pin linearly through the connecting rod eye.